As a tool for helping passengers to walk between floors or reducing a walking distance of passengers, a passenger conveying device is very common in daily life. As an example, escalators generally used between floors of commercial buildings and moving walks generally used in large airports are especially common.
To make it convenient for passengers to take such a type of tool or keep balance, automatic handrails that operate synchronously with the passenger conveying device are provided on two sides of the passenger conveying device for passengers to hold. Many factors are taken into consideration in design of the automatic handrail. For example, the automatic handrail should not be over-tense; otherwise, the automatic handrail strap will be abraded more quickly. On the other hand, the automatic handrail should also not be over-loose; otherwise, the running speed of the automatic handrail strap will be faster than or slower than the speed of steps, which may cause a standing passenger to loose balance or even fall over. Therefore, it is necessary to set the automatic handrail strap within a proper tension degree interval.
In addition, the passenger conveying device is an apparatus having a relatively long service cycle. Therefore, in the service life thereof, it is also necessary to keep monitoring the tension degree of the automatic handrail all the time to detect in time the problem of being loose or too tense caused by various situations during running of the apparatus and to make timely control.